The present invention generally relates to a recording head for an optical storage system, and more particularly, to a recording head employing a solid immersion lens and a method for forming such a recording head.
Optical data storage systems are known. These systems store a high density of information onto an optical recording medium such as an optical disc.
Generally, in optical recording systems employing an optical head, a light source is used to read and write information to/from the optical recording medium. Data is accessed by focusing the beam of light onto one of the data layers of the disc, and then detecting the reflected light beam. The light beam may be focused onto one of the data layers of the optical recording medium by a lens spaced from the medium.
The data density in optical disc drives is determined in part by the diameter of the focussed beam of light on the disc surface, i.e., the spot diameter. The spot diameter may be reduced in order to increase the data density of the optical storage medium. Several methods are known to decrease the spot diameter. One technique is to use light having a shorter wavelength, for example, in the blue region.
Another technique is to increase the effective numerical aperture (xe2x80x9cNAxe2x80x9d) of the lens configured in the optical head. One approach to achieving a high NA lens is to use a lens of high index of refraction (xcex7) material. The lens may be positioned in close proximity to one of the data recording layers on the disc surface. One such lens is a near-field lens, for example, a high refractive index lens with a flat bottom portion, e.g., a solid immersion lens (xe2x80x9cSILxe2x80x9d). In a SIL system, the optical recording medium is spaced from the base of the SIL by a distance of less than one wavelength of the light that is used. This forms a near-field configuration in which the light is coupled by evanescent coupling. The SIL may have the shape of a hemisphere or a supersphere. An air gap typically separates the solid immersion lens and the disc surface. A hemispherical SIL includes a flat portion and a hemispherical portion. For a super-hemispherical lens, the thickness may be less than or about r+r/xcex7, where r is the radius of the partial spherical section. Further details of a hemispherical or super-hemispherical SIL lens may be found in co-pending and commonly owned and assigned U.S. patent application Ser. No. 08/026,907.
A slider can be coupled to the head. The slider may include an air-bearing surface for lifting the slider above the optical disc surface. As the optical recording medium spins, air flows under the air-bearing surface to raise the slider relative to the optical disc surface during read and write operations.
One conventional way of forming an optical head having a SIL is as follows. A sphere of optically transparent material is cut to form a cap lens having a spherical portion and a flat portion. The height of the cap lens may be less than the radius of the original sphere. The flat portion of the cap lens is then positioned into a partial cavity formed in a slider body. Next, the cap lens is secured in the partial cavity by a glue bond formed between the flat portion of the cap lens and the slider body. The slider body and the cap lens may then form a hemispherical SIL. A super-hemispherical lens may also be used, as discussed above. In both configurations, the optical light path includes the SIL, the glue bond, and the slider body.
The above system has certain drawbacks. One drawback is that the material which forms the glue bond may have different optical characteristics than the material of the slider body and the SIL. The phase of the light entering through the spherical surface of the SIL can tend to distort at the glue bond surface because the bond material has a different index of refraction than the slider body and SIL. This causes aberrations in the focussed spot in the optical recording medium, and thus, may reduce the performance of the head. The glue bond may also adversely effect the resolution of the spot diameter. Further, this may result in faulty read and write operations between the optical head and the recording medium.
Another disadvantage is that the SIL is formed separate from the slider body. This requires additional machining tools and components to form the resulting optical head. This tends to increase the cost and labor needed to form these heads.
A coil may also be included in the optical head. A magnetic field generated in the coil can switch magnetic domains in the optical recording medium during a write operation. Heat is generated in each turn of the coil when it is energized by an applied current. In order to achieve a desired magnetic field, the number of turns must be specified.
However, heat generated by the energized coils can cause head distortion. Also, the outermost turns of the coil may not be sufficient to generate a magnetic field in the coil center because they have an increased resistance and inductance.
In one aspect, the present invention is directed to an optical head that includes an optical portion that receives and focuses incoming optical radiation. The optical portion may have a bottom surface adapted to face an optical disk. A magnetic coil may be wound on the bottom surface to have a plurality of turns that have different effective perimeters. The magnetic coil may have a varying property for the different turns such that each of the different turns has substantially the same resistance.
In another aspect, the present invention is directed to an optical head that includes an optical portion that receives and focuses incoming optical radiation. The optical portion may have a bottom surface adapted to face an optical disk. A magnetic coil may be wound on the bottom surface, and may have a plurality of turns that have different effective perimeters. The magnetic coil may have a varying property for the different turns such that the different turns have substantially the same temperature.
Implementations of the above aspects include one or more of the following. The optical portion may include a slider body, a void formed in the slider body, and a solid immersion lens. The solid immersion lens may include a processed flat portion and a spherical portion. The solid immersion lens may be positioned in the void to place the processed flat portion coplanar with the bottom surface. A mesa may be optically coupled to a portion of the processed flat portion of the solid immersion lens, and the coil may be wound around the mesa. The optical head may also include a preformed structure to secure sides of the solid immersion lens to side walls of the void. The preformed structure may be formed from an opaque, a transparent, or a colored glass material. A glue bond may be employed to secure sides of the lens to the sidewalls of the void. The slider body may be formed from a material that is different from the material of the solid immersion lens. The slider body may be formed form the same material as a material of the solid immersion lens. The slider body may be formed from a ceramic material or glass. The solid immersion lens may be formed from cubic zirconia, titanium oxide, beta-silicon carbide, or gallium phosphide. The slider body may be formed from aluminum oxide, calcium titanate, magnesium titanate, silicon, carbide, silicon carbide, or alumina-titanium-carbide. The coil may be rectangular, elliptical, circular, or square. The coil may be a planar coil. The optical head may also include an insulation layer configured to contact the mesa.
In a further aspect, the present invention is directed to a method for fabricating a plurality of optical recording heads. The method includes processing a substrate to form a plurality of voids through the substrate. A sphere of optically transparent material may be placed within each of the voids such that a desired portion of each sphere protrudes from the surface of the substrate. The sphere may be secured to side walls of the void. A portion of the desired protruded portion of the sphere may be removed to form a near field lens, and a mesa may be optically coupled to a portion of the near field lens. A coil may be formed around the mesa, and the substrate may be sliced to form a plurality of optical heads.
Implementations of the invention include one or more of the following. The near field lens may be processed to include a flat portion that is substantially coplanar with the substrate surface. The substrate may be processed to form a plurality of slider bodies such that each of said slider bodies includes one of said voids. The sphere may be secured to said void by a preformed structure. The coil may be formed with a plurality of turns having different effective perimeters. Each of the different turns may have substantially the same resistance. Each of said different turns may have substantially the same temperature. The coil may include a plurality of planar layers. A via may be formed proximate to the mesa to form an electrical contact to the coil.
In a further aspect, the present invention is directed to a method for forming an optical head that includes forming an optical portion that receives and focuses optical radiation. The optical portion may have a bottom surface adapted to face an optical disk. A magnetic coil may be wound on the bottom surface to have a plurality of turns that have different effective perimeters. The magnetic coil may have a varying property for the different turns such that the different turns have substantially the same resistance.
In a further aspect, the present invention is directed to a method for forming an optical head that includes forming an optical portion which receives and focuses incoming optical radiation. The optical portion may have a bottom surface adapted to face an optical disk. The magnetic coil may be wound on the bottom surface to have a plurality of turns that have different effective perimeters. The magnetic coil may have a varying property for the different turns such that the different turns have substantially the same temperature.